"We are not criminals, we are human!"

PHOENIX, Arizona -- Up to 20,000 protesters marched through the southwestern US city of Phoenix on Friday in an explosion of Hispanic opposition to plans for a draconian crackdown on illegal immigrants.

Police said that 15,000 to 20,000 people took part in the Phoenix demonstration, as more than 2,000 high school students staged a classroom walk-out in Los Angeles and Latinos in the southern city of Atlanta rallied and boycotted businesses to protest plans for a legislative assault on immigration.

Fresh protests are scheduled to take place across the country in the coming days, including one in Los Angeles on Saturday that organizers claim will attract hundreds of thousands of people.

Friday's march in the Arizona capital of Phoenix paralyzed the city and surprised authorities, who had expected only about 2,500 protesters against the immigration reform bill to be debated in the US Senate next week.

Opponents have branded the legislation inhumane, unfair, and discriminatory.

"It's racist. The origins of this country are based on immigration. They (immigrants) are looking for a better way of life and to work hard and are a very good benefit to this country," said Mexican immigrant Daniel Ravella, a 42-year-old who has lived legally in the United States for four years.

"I don't agree with the way the immigration law is being passed through the Senate," he told AFP as he marched with his wife and two children.

People clogged the city streets as far as the eye could see, as police on horses, bicycles, and in cars scrambled to control the much larger than expected crowd of angry protesters.

The largely Latino demonstrators, waving US and Mexican flags, chanted and brandished banners and placards with slogans such as "We are not criminals, we are human."

"We march today because we are immigrants, we work hard and we love the USA," said illegal immigrant Carlos Diaz, 25, who has lived in Phoenix for the past five years.

"We are a part of the US. We want amnesty. We want to be residents," he told AFP.

In a possible sign of things to come, one banner unfurled by protesters read: "We are a lot, we will be more."

Some 35 million Hispanics, many of them from Mexico, live in the United States and form the basis of the human machinery that keeps the major cities humming.

Latinos who have gained US citizenship form an increasingly important part of the US electorate and make up 12.5 percent of the total population.

The immigration reform bill to be debated next week, House Resolution 4437, targets illegal immigrants, who number some 11.5 million, according to the Pew Hispanic Center, and account for 24 percent of farm workers, 17 percent of cleaners, and 14 percent of construction workers.

The law would make all undocumented immigrants criminals and require all employers to verify the immigration status of their employees.

The US House of Representatives has already passed the bill, and Republican Senator Bill Frist has introduced a companion bill in the Senate that also would make it a felony to be in the United States without the proper paperwork.

It comes amid growing US security fears and as conservatives complain of illegals stealing American jobs.

In Latino-dominated areas of Los Angeles, thousands of high school pupils walked out of class en masse to protest the beefed up enforcement of immigration laws, marching through nearby streets.

"They're making laws for all immigrants to go back to their countries, and we just think that's not right," student Francisco Velazquez said. "We all want to stay here. We all want to get a good education."

In the southern city of Atlanta, where about four percent of the population is Hispanic, immigrant business owners closed their shops and boycotted those that remained open.

The proposed law would also increase penalties for immigrant smuggling, stiffen those on undocumented immigrants who reenter the United States, and crack down on anyone giving succor to undocumented residents, including churches.

Another proposition under debate is the construction of an 80-kilometer (50-mile) wall sealing part of Arizona's 320-kilometer (200-mile), porous border with Mexico.

Mexican framer and carpenter Martin Ramirez, 41, who has lived without papers in the United States for 23 years, said during the Phoenix march that he had not come to America to live off the state.

"I came to work for the kids, for a better life, I didn't come for food stamps," he said.

A wave of protests against the proposed law has rolled across the country, culminating in a protest of up to 30,000 people who marched through the streets of the Midwestern city Milwaukee on Thursday in a protest dubbed a "day without Latinos."